A conventional distributed antenna system (DAS) provides indoor coverage for wireless communications. Transmitted power is divided among several antennas in distributed indoor locations so as to provide a large coverage area using less transmitted power than would be required by a single antenna system. The antennas of a typical DAS are connected to a cellular base station and are used for cellular mobile communications.
A DAS can be implemented using passive or active components. A passive DAS is implemented using passive splitters and, to minimize signal degradation between the base station and antennas, large diameter coaxial cables are typically employed. Installation of a conventional passive DAS requires a planning phase that includes site surveys and system set-up by trained experts in order to ensure that the coverage area and signal strength is suitable throughout the system. Accordingly, passive DAS systems tend to be expensive to implement.
An active DAS employs active amplifiers and, in some cases, frequency converters that reduce a radio frequency (RF) signal from the base station to an intermediate frequency (IF) for communication to antenna units. At the antenna units, the IF signals are up-converted to RF again. Such active DAS implementations require only thin coaxial cable, though the performance tends to be improved over that of passive DAS implementations. So that the active DAS is able to accommodate various communication channels and frequencies used by mobile equipment and base stations, the active components need to process a wide range of frequency bands. Due to the requirement for active components that process a wide range of frequency bands, active DAS systems also tend to be expensive to implement.
Therefore, what is needed is an improved distributed antenna system. It is toward this end that the present invention is directed.